# CVE-2026-89549: sunrpc: route to a populated pool in svc_pool_for_cpu()

> An attacker can cause indefinite connection hangs in NFS services by exploiting thread pool routing flaws when thread counts are lower than NUMA nodes.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100421, BELL-CVE-2026-89549, DEBIAN-CVE-2026-89549, GHSA-j6w6-qx29-46gg, UBUNTU-CVE-2026-89549

## What is CVE-2026-89549?

CVE-2026-89549 is a high-severity denial of service vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

sunrpc: route to a populated pool in svc_pool_for_cpu()

svc_set_num_threads() spreads the requested threads evenly across the
service's pools (base = nrservs / sv_nrpools).  When a service runs
fewer threads than it has pools -- e.g. an nfsd configured with fewer
threads than the host has NUMA nodes while running in "pernode" or
"percpu" mode -- the trailing pools are left with no threads at all.

svc_xprt_enqueue() selects a pool from the CPU servicing the transport,
queues the transport on that pool's sp_xprts, and only wakes a thread
from the same pool.  Each thread services exclusively its own pool, so a
transport that lands on a threadless pool is enqueued on sp_xprts and
never picked up: the connection hangs indefinitely.

Have svc_pool_for_cpu() skip pools that currently have no threads,
falling back to the next populated pool.  This trades NUMA locality for
a guarantee that the work is actually serviced.  sp_nrthreads is only
updated under the service mutex; the lockless read here is a best-effort
routing hint, so annotate it with data_race().

## Which versions are affected by CVE-2026-89549?


## How do I fix CVE-2026-89549?

Apply the vendor's patch.

## Is CVE-2026-89549 being exploited?

There is no known exploitation of CVE-2026-89549 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89549 and fix it if it is affected.

What it is: CVE-2026-89549 is a high-severity denial of service vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89549 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89549/ (Markdown: https://insights.sbomify.com/CVE-2026-89549/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89549
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89549
- OSV: https://osv.dev/vulnerability/CVE-2026-89549

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89549/
Summaries are generated and may contain mistakes; the official description above is the record.